JPH081804B2 - Internal reforming molten carbonate fuel cell - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Use of the Invention The present invention relates to an internal reforming molten carbonate fuel for directly supplying hydrocarbons and steam into a fuel cell to simultaneously perform steam reforming and power generation of hydrocarbons. Regarding batteries.

[Background of the Invention]

A fuel cell generally has a structure in which an electrolyte is sandwiched between a fuel electrode and an oxidizer electrode. For example, hydrogen is supplied to the fuel electrode and oxygen is supplied to the oxidizer electrode to take out direct-current power from between the two electrodes. In the molten carbonate fuel cell, a mixed molten salt of lithium carbonate, potassium carbonate, etc. is used as an electrolyte, and carbonate ions (CO ₃ ²⁻ ) serve as charge carriers. A porous plate mainly composed of nickel is used for the fuel electrode, and a porous oxidized nickel plate is used for the oxidizer electrode. A fuel such as H ₂ is supplied to the fuel electrode to cause the reaction of formula (1), and O ₂ and CO ₂ are supplied to the oxidant electrode to cause the reaction of formula (2), resulting in 2e− electricity. Generate energy.

^{_{H 2 + CO 3 2 - →}} H 2 O + CO 2 + 2e- ... (1) In a molten carbonate fuel cell, conventionally, a fuel gas flow path in contact with a fuel electrode is filled with a reforming catalyst, and hydrocarbon gas is directly supplied together with water vapor to reform into H ₂ , and the generated H ₂ is used as fuel for electricity. A method of obtaining energy is known. This system is called an internal reforming type fuel cell. Since the reforming reaction has an endothermic reaction, the heat generated by the battery reaction can be utilized, which is advantageous in that the cooling load of the battery can be reduced. Further, the reforming device placed outside can be omitted, which is advantageous in that the system can be simplified.

Conventionally, in an internal reforming type molten carbonate fuel cell, a granular, pellet-shaped or lump-shaped reforming catalyst is formed in a fuel gas channel formed by a fuel electrode and a fuel channel plate (separator), which is in contact with the fuel electrode. A nickel-based catalyst is packed (for example, Japanese Patent Publication No. 47-25782 and Japanese Patent Publication No. 49-7928).
issue). However, these catalyst-packed beds structurally have a large pressure loss with respect to the fuel gas pressure, and depending on the reaction conditions, soot-like carbonaceous substances tend to mainly form along with the hydrocarbon reforming reaction. , This accumulates in the catalyst packed bed and increases the pressure loss of the catalyst bed, and the gas pressure in the fuel gas inlet region becomes high, which causes imbalance with the oxidizing gas pressure on the oxidizer electrode side, and finally the oxidizer electrode A dangerous situation may occur in which fuel gas leaks into the side through the electrolyte plate.

Further, in the fuel cell, in order to support the electrolyte plate and bring the electrolyte plate into close contact with the fuel electrode and the oxidizer electrode, a fuel flow path plate having a large number of ribs on the fuel gas flow path side is generally used. Alternatively, a corrugated sheet-shaped fuel supply channel is also used for close contact (for example, Chemical Ome Point8, fuel cell, issued April 1, 1984, Takehiko Takahashi, PP106, Kyoritsu Publishing Co., Ltd.). A large number of processing man-hours are required for manufacturing these, and there is a drawback that the cost becomes high.

In addition, in Mitsubishi Electric Technical Report (Vol, 58, No.9, P.656,1984), a fuel electrode having many ribs on the fuel current path side is used.
A conceptual diagram of an internal reforming fuel cell in which massive reforming catalysts are filled between the ribs is shown. In the above-described cell structure, the packed catalyst layer essentially increases the pressure loss, and the fuel gas flow path is blocked due to the generation of soot.

On the other hand, JP-A-58-10374 discloses that a catalyst layer held by a corrugated member having air permeability such as a perforated plate is placed without covering the entire cross section of the fuel gas passage. However, there is a drawback in that a complicated corrugated member having air permeability for holding the catalyst is required.

Further, in all of the above-mentioned conventional examples, the reforming catalyst is in contact with the fuel electrode plate, and the pores of the reforming catalyst are covered by the molten carbonate that penetrates through the fuel electrode plate, or the catalyst carrier and the carbon dioxide It has a serious disadvantage that the salt reacts with the substance to be transformed into another substance and the modifying activity is lowered in a short time. For example, a nickel-based catalyst having alumina as a carrier is known as one of the reforming catalysts. Alumina (Al ₂ O ₃ ) reacts with lithium carbonate (Li ₂ CO ₃ ) as an electrolyte component to obtain lithium aluminate. It is known that the property of conversion to (LiAlO ₂ ) deteriorates the reforming activity remarkably.

[Object of the Invention]

It is an object of the present invention to provide an internal reforming molten carbonate fuel cell which is free from the possibility of clogging of the fuel gas passage and has less activity deterioration of the reforming catalyst.

[Outline of Invention]

In the internal reforming molten carbonate fuel cell of the present invention, a fuel electrode plate and a flat plate-shaped catalyst member are provided as separate bodies, and the flat plate-shaped catalyst member is maintained in a predetermined space with respect to the fuel electrode plate. It is provided with a means for supporting and facing each other and using the facing interval as a fuel gas passage.

Further, the flat catalyst member is in the form of particles, pellets,
Alternatively, a lumped reforming catalyst is formed in a flat plate shape and a porous member is used as a core material, and a part of the core material of the porous member is formed in a flat plate shape so as not to block the space of the fuel gas passage. It is formed by forming a protrusion protruding from the reforming catalyst to the side of the fuel electrode plate, and the protrusion of the core material of the plate-shaped catalyst member is used as a spacer in the space between the fuel electrode plate and the plate-shaped catalyst member. A fuel gas flow path is formed.

The internal reforming molten carbonate fuel cell according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a sectional view showing an internal reforming molten carbonate fuel cell of the present invention in the form of a unit cell, FIG. 2 is a vertical sectional view taken along the line AA of FIG. 1, and FIG. Fig. 4 is a perspective sectional view of the reforming catalyst, and Fig. 4 is an exploded perspective view of the essential part of the fuel cell according to the present invention. The same parts are designated by the same reference numerals.

An electrolyte plate 10 is sandwiched between the fuel electrode plate 11 and the oxidizer electrode plate 12 so as to be in close contact with them. Each electrode is provided with collector plates 51, 52 on the side of the supplied gas in order to enhance the collector effect. A flat plate-shaped reforming catalyst 22 formed by using a wire mesh and a porous plate as a core material 23 is loaded on the fuel electrode side, and a fuel gas passage 20 is formed between the catalyst and the fuel electrode 11. The core material 23 of the catalyst is exposed to the outside of the catalyst at certain intervals, and a plurality of protrusions 24 having a height corresponding to the thickness of the fuel gas passage are formed. The protruding portion 24 secures a fuel gas flow path without blocking the space where the reforming catalyst 22 and the fuel electrode 11 face each other in the flow direction of the fuel gas as a spacer, and also secures the fuel electrode 11 and further the electrolyte plate 10. To support. The fuel channel plate 21 is a reforming catalyst 22.
Are opposed to the fuel electrode 11 while maintaining a predetermined space, and the fuel gas is sealed. As shown in FIG. 2, the fuel fluid plate 21 has a supply hole 25 for the hydrocarbon gas 40 and the steam 41.
And a discharge hole 26 is provided.

A flow path for the oxidizing gas 43 containing O ₂ and CO ₂ is provided on the side of the oxidizer electrode plate 12.
30 is formed by the oxidant gas flow channel plate 31. The oxidizing gas flow path plate 31 has a supply hole 32 and a discharge hole 33 for the oxidizing gas 43.
Is provided.

The reforming catalyst 22 has a flat plate shape, and the pressure loss of the fuel gas flow path 20 is extremely low as compared with a conventional catalyst packed bed such as a granular shape,
Further, it is not clogged due to the formation of soot-like substances. Further, since the protruding portion 24 of the core material of the reforming catalyst functions as a spacer, the reforming catalyst does not come into direct contact with the fuel electrode 11 and prevents penetration of the molten carbonate from the electrolyte plate 10 through the fuel electrode. The deterioration of the catalytic activity due to electrolytic carbonate is suppressed.

The core material serves to shape and maintain the catalyst in a flat plate shape. The core material needs to be corrosion resistant, and for example, a stainless steel wire net or a perforated plate is used.

In the above structure, the hydrocarbon gas 40 is supplied to the fuel gas passage 20 through the supply hole 25 together with the water vapor 41, contacts the reforming catalyst 22, and is reformed at a fuel cell operating temperature of about 650 ° C. Natural gas is generally supplied as the hydrocarbon gas. Methane, which is the main component of natural gas, produces H ₂ by the reforming reaction of equation (3).

CH ₄ + 2H ₂ O → 4H ₂ + CO ₂ (3) The reforming catalyst is a nickel-based flat plate that is formed by applying or press-bonding the catalyst material to the core material and firing it, and then loading it into the fuel gas flow path. . Lithium carbonate (Li
₂ CO ₃ ), potassium carbonate (K ₂ CO ₃ ), sodium carbonate (Na ₂
A substance that is stable to carbonates such as CO ₃ ) is selected. In particular, it is known that magnesia and lithium aluminate are stable against carbonates. In order to form them into a molded product having a certain strength, it is necessary to perform baking after the above-mentioned coating or pressure bonding, and these steps are carried out outside the battery.

Oxidizing gas 43, which is a mixture of air and CO ₂ , is supplied from the supply hole 32 to the flow path 30 on the oxidizer electrode plate 12 side. The electrolyte plate 10 is a mixed carbonate of lithium carbonate and potassium carbonate, through which the carbonate ion CO ₃ ²⁻ moves, and in the fuel electrode plate 11, H ₂ generated by reforming methane and (1) The reaction of the formula occurs. On the other hand, in the oxidizer electrode plate 12, oxygen in the supplied air and CO ₂ cause a reaction of the formula (2) to occur, and CO ₃ ² − is replenished. By these reactions, 2e− electricity is generated by using CO ₃ ²⁻ as a charge carrier and is taken out as DC power. In this embodiment, the core material such as the wire mesh is partially projected outside the flat catalyst and used as a spacer, but a spacer can be used separately.

Fig. 5 shows two layers of core wire mesh and perforated plate (23,2
3 ') shows a flat catalyst. With this structure, a large amount of catalyst material can be retained, and the strength of the plate-shaped catalyst can be increased.

Example of Invention

 Examples of the present invention will be described below.

Example A square cell having an electrode area of 50 cm ² as shown in FIGS. 1 to 4 has a thickness of 1.5 m as shown in FIG.
In m, a flat-shaped reformed catalyst in which the protruding height and the width of the protruding portion 24 of the core material are 3 mm is loaded. The core material was a double wire mesh made of stainless wire with a diameter of 0.2 mm and having an opening of about 0.4 mm (35 mesh). The catalyst is a nickel-based commercially available granular catalyst with alumina as a carrier, which is finely pulverized, and then made into a paste, pressure-bonded to the above core material, and molded into a flat plate, 800
It was baked for 2 hours at ℃. The protrusions of the core material were provided at intervals of 20 mm in parallel with the flow of fuel gas.

In the above, methane was supplied at a rate of 3 / h under the conditions of atmospheric pressure, 650 ° C., and steam / metal molar ratio of 3 to generate electricity. As the oxidizing gas, air mixed with 30% of CO ₂ was supplied. As a result, the dry standard hydrogen concentration at the battery outlet was 68% at a load with a current density of 150 mA / cm ² ,
Even with the continuous test of time, the hydrogen concentration hardly decreased.

The nickel-based catalyst using alumina as a carrier in this example is used to clarify the relationship with the comparative example described below, and a carrier having carbonate resistance is used originally.

Comparative Example In a single cell having the same electrode area of 50 cm ^{2 as in} the example, instead of loading the flat catalyst according to the present invention, a commercial granular catalyst of the same lot before pulverization (particle size of about 3.5 mm) in the example was directly filled. . In the above, power generation test was performed by supplying methane under the same conditions as in the examples. As a result, when the current density was 150 mA / cm ² , the dry standard hydrogen concentration at the battery outlet was 68% at the beginning of the test, but then gradually decreased to 52% after 150 hours and 40% after 250 hours. It became difficult to generate electricity under the above load.

After the test, the granular catalyst was taken out and analyzed.
Lithium and potassium, which are constituents of the electrolyte plate, were detected at 1.9 and 9.4 wt% respectively, and it was clarified that the decrease of catalytic activity was due to the infiltration of carbonate.

〔The invention's effect〕

As shown in the examples, according to the present invention, it is possible to suppress the activity deterioration of the reforming catalyst loaded in the cell, achieve a long life of the internal reforming fuel cell, and improve the reliability. be able to. Also, without the accumulation of soot-like substances,
It is possible to prevent the danger due to blockage. Further, it is not necessary to provide a rib for supporting the electrolyte plate on the fuel electrode side fuel flow channel plate, and the fuel flow channel plate can be manufactured at low cost.

[Brief description of drawings]

1 is a cross-sectional view of an internal reforming molten carbonate fuel cell of the present invention, FIG. 2 is a vertical cross-sectional view taken along the line AA of FIG. 1, FIG. 3 is a cross-sectional perspective view of a flat catalyst, FIG. 4 is an exploded perspective view of constituent parts of the fuel cell of FIG. 1, and FIG. 5 is a sectional perspective view of another flat catalyst. 10 ... Electrolyte plate, 11 ... Fuel plate, 12 ... Oxidizer plate,
20 …… Fuel gas flow passage, 21 …… Fuel flow passage plate, 22 …… Flat reforming catalyst, 23 …… Core material, 24 …… Projecting portion, 40 …… Hydrocarbon gas, 41 …… Steam, 51 , 52 …… Current collector.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Makoto Shimoda 4026 Kuji Town, Hitachi City, Ibaraki Prefecture, Hitachi Research Laboratory, Hiritsu Manufacturing Co., Ltd. (56) References JP 61-260555 (JP, A)

Claims (3)

[Claims] 1. An internal reforming molten carbonate fuel cell in which a flat plate-shaped catalyst member is opposed to a fuel electrode plate at a predetermined interval, and the facing interval between the fuel electrode plate and the flat plate-shaped catalyst member is a fuel gas flow path. In the above, the fuel electrode plate and the flat plate-shaped catalyst member are provided as separate bodies, and the flat plate-shaped catalyst member forms a particulate, pellet-shaped, or lump-shaped reforming catalyst in a flat plate shape, and a porous member is used as a core material. The reforming catalyst having a part of the core material of the porous member formed in a flat plate shape so as not to block the space of the fuel gas flow path, and forming a protruding portion protruding toward the fuel electrode plate side. An internal reforming molten carbonate characterized in that a fuel gas flow channel is formed in the space between the fuel electrode plate and the flat plate-shaped catalyst member using the protrusion of the core material of the flat plate-shaped catalyst member as a spacer. Fuel cell. 2. The internal reforming molten carbonate fuel according to claim 1, wherein the porous member constituting the core material of the flat catalyst member is one of a wire mesh and a porous plate. battery. 3. The internal reforming molten carbonate fuel cell according to claim 1 or 2, wherein the porous member forming the core material of the flat catalyst member is a double stack. .